Exploring Negative Absolute Temperature Using NetLogo

Abstract

The possibility of negative temperatures on the Kelvin scale is intriguing and confusing simultaneously. This is because students are used to thinking of temperature as a measure of the internal energy of a system. While this concept is good for many systems, it does not work for all systems. Nuclear and electron spin systems, along with lasers and other energy-bound systems, have negative absolute temperature. These systems have an upper limit to their energy, which arises out of the quantum nature of these systems. This is what gives rise to the negative absolute temperature. Temperature in the broadest sense is related to the change of the entropy of a system for a given change in the internal energy of the system. To help students understand this concept, we have developed a NetLogo model simulation of a binary spin lattice system using the 2D Ising model. For example, imagine a grid of tiny suspended bar magnets, with each magnet only allowed one of two orientations: north pole up or south pole up. NetLogo is a software tool that allows users to program agents that can interact with each other and the environment. Through using this simulation, students in a calculus-based physics or thermodynamics class will get a visual and hands-on experience of the full range of temperatures possible.